1. Field of the Invention
The present invention relates to a speech recognition apparatus for recognizing the voice of a speaker entered through a voice input means, such as a microphone or the like, and more particularly to a speech recognition apparatus suitable for use in controlling a vehicle-mounted electronic unit based on speech recognition technology. In the speech recognition system, the speech recognition rate of speech, which exists together with background car audio sounds, is not lowered, by employing a microphone with high directivity. The present invention also concerns a vehicle incorporating such a speech recognition apparatus.
2. Description of the Related Art
Modern vehicles are equipped with many electronic units, which are constantly growing to provide higher functionality. Under such circumstances, speech recognition apparatuses have been proposed for generating remote control commands based on speech recognition, in order to easily control various electronic devices such as a navigation system, an audio system, or an air-conditioning system, which are incorporated in the vehicles.
As has been pointed out, when the voice of a speaker is input to a microphone of a speech recognition apparatus in a vehicle that is also equipped with an audio system, sounds from loudspeakers of the audio system are also input to the microphone, thereby lowering the speech recognition rate of the speech recognition apparatus (see, Japanese Laid-Open Patent Publication No. 2000-132200).
According to the audio/video system disclosed in Japanese Laid-Open Patent Publication No. 2000-132200, the above problem is solved by providing two loudspeakers mounted in a front region of the vehicle and two loudspeakers mounted in a rear region of the vehicle, and further wherein the speech recognition apparatus incorporated in the audio/video system includes a microphone embedded in the steering wheel of the vehicle. When the speech recognition apparatus operates to recognize the voice of the speaker, music sounds output from the two loudspeakers in the front region of the vehicle are attenuated within a speech frequency band, because they produce an adverse effect on the microphone in the steering wheel, and during speech recognition music sounds are radiated primarily from the two loudspeakers located in the rear region of the vehicle.
However, the disclosed speech recognition apparatus has the following disadvantage. When the audio/video system operates such that main vocal sounds are radiated only from the two loudspeakers, (e.g., left and right loudspeakers) in the front region of the vehicle, and main melody sounds are radiated only from the two loudspeakers in the rear region, the main vocal sounds become muted in the speech frequency band by the speech recognition apparatus, thereby developing an unnatural music sound environment in the passenger compartment of the vehicle. Conversely, when main melody sounds are radiated only from the two loudspeakers in the front region of the vehicle, and main vocal sounds are radiated only from the two loudspeakers in the rear region, the main melody sounds become muted in the speech frequency band by the speech recognition apparatus, thus also developing an unnatural music sound environment in the passenger compartment of the vehicle.
If only two loudspeakers, e.g., left and right, for stereophonic sound reproduction are installed in the passenger compartment of the vehicle, and the microphone embedded in the steering wheel has a directivity pattern covering the driver's seat, then only sounds radiated from the loudspeaker near the driver's seat may be muted by the speech recognition apparatus. However, this type of sound muting also develops an unnatural music sound environment in the passenger compartment.
Similar problems arise if the conventional speech recognition apparatus is combined with a 5.1-channel surround system. Specifically, the 5.1-channel surround system is capable of outputting independent sounds from respective loudspeakers for producing surround sound effects. If the sounds from certain loudspeakers of the 5.1-channel surround system are muted, then an unnatural and odd music sound environment is developed in the listening space. Therefore, when the conventional speech recognition apparatus is combined with a 5.1-channel surround system, the apparatus is required to attenuate the sounds in all channels by −20 dB, for example, when the voice of a speaker is input for speech recognition.